Aryl sulfonic acid catalysts: Effect of pendant group structure on activity in hydrolysis of polyethylene terephthalate

• Published in: Journal of applied polymer science Vol. 139; no. 27
• Main Authors: Abedsoltan, Hossein, Coleman, Maria R.
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 15.07.2022; Wiley Subscription Services, Inc
• Subjects: Acids; Aromatic compounds; Catalysts; degradation; Ethyl acetate; Hydrolysis; Inorganic acids; kinetics; Materials science; polyesters; Polyethylene terephthalate; Polymers; recycling; Sulfonic acid; Sulfuric acid; Wetting
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.52451

A series of aryl sulfonic acids were tested as catalysts for acid hydrolysis occurring at the surface of poly(ethylene) terephthalate (PET) particles. Specifically, p‐toluenesulfonic acid monohydrate (PTSA), 2‐naphthalenesulfonic acid (2‐NSA), and 1,5‐naphthalenedisulfonic acid tetrahydrate (1,5‐NDSA) were chosen to provide sulfonic acid active groups and varying hydrophobic functionality. The effect of catalyst concentration and reaction temperature on PET hydrolysis rate was studied. The aryl sulfonic acid catalysts exhibited much higher rates of PET hydrolysis than the mineral acid, H2SO4. At 150°C and 4 M catalyst, the time required to achieve more than 90% TPA yield was 3, 3, and 8 h, and 18 h for (PTSA), (2‐NSA), (1,5‐NDSA), and H2SO4, respectively. Ethyl acetate hydrolysis was performed as a model reaction to probe the activity of the catalysts in homogenous reactions to compare with the heterogenous hydrolysis reaction occurring at the PET surface. The higher catalytic activities for PET hydrolysis of the PTSA, 2‐NSA, and 1,5‐NDSA than H2SO4 was attributed to improved wetting by the reaction media and affinity of the aryl sulfonic acid catalysts for the PET surface. The wide use of poly(ethylene terephthalate) (PET) for single use packaging and textiles has led to a need for broader recycling methods. Chemically depolymerizing waste PET into base monomers is an attractive alternative to traditional mechanical recycling. This paper focuses on the effect of catalyst structure on acid hydrolysis of the PET surface. Catalysts with hydrophobic pendant groups exhibited an affinity for the PET flake surface and improved depolymerization kinetics.